'Flat' is not correct for a stereo system ?

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SL recently wrote:

Experiences with equalizing an initially flat on-axis response to obtain the realistic sounding ORION-3.2 have convinced me that 'flat' is not correct for a stereo system. Here we must create believable phantom sources from two real sources at +/-30 degree angle to the listener, at the 'sweet spot', in the room. Nor is the BBC dip the answer. Instead, the response must be flat above 100 Hz and then gradually drop to a lower level at high frequencies. There are general physical and psychoacoustic requirements for such a response, which I will explain at a later time. A specific on-axis frequency response curve is usually the secret behind a good sounding loudspeaker. The marketing department likes to label this curve 'flat'.

Linkwitz-Links

I'm about few thousands kilometers from my speakers so I have yet to build and see/hear this curve for myself. But is it reaaally ??
 
Interesting!! This tends to fit with my preferrences for a slightly subdued treble response! I find that when I adjust for flat treble response I don't like the sound, when it is slightly more subdued than 'flat' I find the speakers much more enjoyable 🙂

Of course since my microphone isn't calibrated (WM-60AY so pretty flat usually) it is hard to say whether what I've measured is a true representation....

Tony.
 
I like to roll-off my treble by a dB or so too. In the thread above, JohnK says he does something similar. I think others do too, and I strongly suspect it has to do with the room one is listening in, and personal preferences.

One should note that there is a backstory to SL's observations, that is discussed in the above thread.
 
SL recently wrote:

Experiences with equalizing an initially flat on-axis response to obtain the realistic sounding ORION-3.2 have convinced me that 'flat' is not correct for a stereo system. Here we must create believable phantom sources from two real sources at +/-30 degree angle to the listener, at the 'sweet spot', in the room. Nor is the BBC dip the answer. Instead, the response must be flat above 100 Hz and then gradually drop to a lower level at high frequencies. There are general physical and psychoacoustic requirements for such a response, which I will explain at a later time. A specific on-axis frequency response curve is usually the secret behind a good sounding loudspeaker. The marketing department likes to label this curve 'flat'.

Linkwitz-Links

I'm about few thousands kilometers from my speakers so I have yet to build and see/hear this curve for myself. But is it reaaally ??

I think at this point you have to take some of what SL says with a grain of salt. This argument about flat on axis response has a lot more to do with what is happening off axis and total power response as well as room acoustics. SL's comments are made with respect to the current "tuning" of the Orion. I believe a lot of this has to do with the mismatch of the polar response above the crossover from dipole mid to dome tweeter. I see the same thing in the NaO II. In a live environment it can sound a little bright which is why the NaO II has always had a tweeter level control.

I recently did an experiment listening to the NaO II side by side with the NaO Note. As you may be aware, the NaO Note maintains dipole response to a much higher frequency than either the NaO II or the Orion, and above 4k hz the polar pattern begins to narrow. You can view the polar response of the NaO II here and Note here. When I initially listened to the Note beside the NaO II the note sounded different, more so than I expected. The NaO II has a highly detailed and somewhat etched sound to it, much like an ELS. Not surprising as I used my Martin Logan Monoliths as a reference. (One of the goals of the NaO II was to sound similar to the Monolith but without the large panel beaming.) Thankfully, the Note sounded more natural, still highly detailed but not so ELS like. Still I wanted to understand the source of the difference. So what I did was to digitally equalize both main panels to have a 100 Hz LR4 high pass response which was ruler flat on axis and also matched the on axial levels. Thus all that remained was the effects of polar response. The difference between the NaO II and the Note remained. But what was interesting was that I could make the Note sound very much like the NaO II by boosting the response above 3k Hz. Similarly I could make the NaO II sound similar the Note by shelving down the response above 3k Hz. What this tells me is that at higher frequency it seems to be more about power response than on axis response. Thus messing with the on axis response at higher frequency seems more to be compensating for the behavior of the polar response. It is not so much that the on axis response should droop at higher frequency. It is that the power response should. This can be achieved by keeping the on axis response flat while narrowing the polar response. In the case of the Orion, my opinion is that SL is actually compensating for the broadening of the polar response above the crossover by shelving down the tweeter level.

I don't think this should come as any surprise. After all, take a speaker that sounds good in a highly damped environment and place it in a highly reflective environment and what do you do? Turn down the treble.

SL's comment, "A specific on-axis frequency response curve is usually the secret behind a good sounding loudspeaker" has more to do with what the polar response of the speaker is than what the on axis response is, IMO. Otherwise all we would need to do is measure the on axis response of that mythical good sounding speaker and all speakers with the same on axis response would sound the same. Obviously, if the on axis response must be tailored based on the speakers polar response to yield the correct power response then the inverse should also be true; for a given power response we should be able to tailor the polar response so that the on axis response is flat. This is what I have attempted to do with the NaO Note. As you may be aware I have been adamant about trying to correct the discontinuity in the polar response of speakers like the NaO II and Orion for some time. I believed the solution was to start with a clean sheet of paper which is what the NaO Note is all about.
 
SL recently wrote:

Experiences with equalizing an initially flat on-axis response to obtain the realistic sounding ORION-3.2 have convinced me that 'flat' is not correct for a stereo system.

Correlation does not imply causality. I think it's more likely that we're looking for a reduction in the total direct and reflected energy towards high frequencies which can also come from flat-on axis response with monotonically increasing directivity.

IIRC Toole and Olive's research suggests that our brains form their impression of timbre as a combination of the direct sound and what we identify as reflections.

That explains empirical observations of speakers with flat on-axis response and broadening polar response towards high frequencies being perceived as bright which can be tamed by non-flat response.

Since the Orion front hemisphere polar response broadens from 800Hz - 4KHz, it should need some on-axis attenuation.

As a counter-example, Pluto works great with flat on-axis response until the last octave and monotonically increasing directivity.
 
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ignoring the stereo issue, we have on axis, off axis and the so called energy response. Then there is room influence and furthermore in case of a multiway speaker the drivers must add properly at listening position.
Developing a speaker for having a flat on axis response in an anechoic chamber with microphone at tweeter height in 1m distance is unlikely to give good sound.
regards
 
If Linkwitz is "fixing" a directivity issue, then EQ may not be the optimum approach....:scratch2:

That would be my point. The correct approach is to start with a clean sheet of paper. Fix the directive problem.

There are a number of factors 1) on axis response, 2) directivity, 3) Power (or Energy), 4) the ratio of direct to reflected sound, and 5) room absorption/reflection (RT60 for example), and others. If we assume that RT60is reasonably constant vs frequency for a room then the ratio of direct to reflected (d/r) sound will be a function of the power response, on axis response and listening distance. At a given listening position d/r is fixed and any variation with frequency becomes a function of the radiated power and the on axis response. If you are sitting at a distance where the reverberant sound is dominant then peaks or valleys in the reverberant sound are due to peak or valleys in the power response. Power response is a function of the on axis response and the radiation pattern. So if there is a problem in the reverberant field the choice is to either change the radiation pattern or change the on axis response. The problem, IMO with just changing the on axis response is that it keeps the d/r ratio constant. If you are past the critical distance and the reverberant field is dominant then this may not be a problem. But if you are inside the critical distance , where the direct sound become more dominant changing the on axis response is likely to cause problems. It is most likely that the more desirable approach is to fix the radiation pattern so that a flat on axis response yields the correct power response vs frequency. Of course, then you have to ask what is the correct or necessary power response required to generate the desired reverberant field is a given room? Sinc e the room is not constant there can be no universally correct polar response or frequency response. It will be room dependent.

The experiment I did with the NaO II and NaO Note clearly shows that flat frequency response is not necessarily the villain. It showed that two speakers with identical on axis response can sound significantly different solely due to the differences in polar response and radiated power.
 
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I like to have 4dB increase on treble. This to have a better average flat response of axes.

A normal tweeter increase SPL on-axes off-axes they drop below flat response. It doesn't sound correct to me flat on axes. Maybe I have become a bit deaf?

I started to measure what I have on listening position, ever sins I have the MLS gear for it that shout be the leading goal.
 
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Excellent post John! One of the most sensible on the subject I've read. My personal experience would say that the decay of the bass is not that important.

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This doesn't sound muddy or anything. The only area where I really haven't been able to hear a difference in a large RT60 time change is the bass/midbass.

I know in some recording studios they try to keep the decay times spectrally similar. Makes good sense.

removing the treatments will add a bit more life:
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but this difference doesn't seem large enough to severely alter the tonal balance. Just a small change really. Maybe with a more narrow pattern you might be able to make it sound like before.

Dan
 
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